Browsing by Author "Iliev V."

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    Dielectric and microwave properties of siloxane rubber/carbon black nanocomposites and their correlation
    (2011-01-01) Al-Hartomy O.A.; Al-Solamy F.; Al-Ghamdi A.; Dishovsky N.; Iliev V.; El-Tantawy F.
    In this paper, the dielectric and microwave properties of carbon black/siloxane rubber-based nanocomposites have been investigated in the frequency range from 1 GHz till 12GHz according to the content of carbon black and the frequency. It has been established that the increasing frequency and filler content lead to an increase in the relative permittivity and tangent of dielectric loss angle. At higher filler content, the effects become more pronounced, especially those upon dielectric loss. It has been also established that there are two well-distinguished areas in all dependences of microwave properties on frequency and filler content increasing. The first is between 1 and 8 GHz wherein the reflection and attenuation of microwaves do not change considerably with frequency and filler content alternation while shielding effectiveness worsens. The second area is between 8 and 12 GHz wherein the reflection and attenuation of microwaves increase drastically with the increasing frequency and filler content. Shielding effectiveness improves, too. It has been established that in all cases the degree of correlation between dielectric and microwave properties evaluated on the basis of the coefficients of correlation calculation is perfect. Copyright © 2011 Omar A. Al-Hartomy et al.
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    Gas hold-up prediction in gas - liquid stirred tank reactor using CFD simulation
    (2014-01-01) Stoykova R.; Moutafchieva D.; Popova D.; Iliev V.
    This paper presents results from CFD simulation of gas-liquid mixing in an aerated stirred tank reactor. The ANSYS CFX simulation program method has been used to predict the distribution of the overall gas hold-up in gas-sparged tank with 1000 l work volume, equipped with two six-blade pitched turbines and a ring sparger of 0.41 m diameter. Fluid flow is calculated with a turbulent k - ε two fluid model using a finite volume method. The CFD simulation results indicate that the method used is suitable for the prediction of the change of overall gas hold-up with increasing both of the impeller speed and the gas flow rate.
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    Numerical simulation of bubble breakup and coalescence in bubbling two-phase flow
    (2018-01-01) Moutafchieva D.; Iliev V.
    The aim of the present work is to study the behavior of gas-liquid bubbly flow by means of Computational Fluid Dynamics (CFX ANSYS). The population balance approach taking into account the bubble coalescence and breakup in turbulent gas-liquid dispersion is included.The Euler-Euler approach and the standard k-ε mixture turbulence model in three-dimensional computational domains accounting the effect of turbulence are used to simulate the two phase flows of the bubble column.The bubble size distribution along the column height, the gas volume fraction and liquid velocity have been predicted for the two-phase systems and for liquids different from water(ethanol, glycerol). The results of nonuniform bubbles size distribution in dispersed flow are presented grouped into individual size fractions at varying initial conditions and density of the elementary mesh.
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    Stress analysis of insulating glass units under transient thermal loadings
    (2018-01-01) Ivanov I.; Velchev D.; Penkova N.; Krumov K.; Iliev V.
    Finite element stress analysis of glass panels in insulating glass units (IGU) is carried out based on the temperature field determined by serial numerical simulations of the conjugate heat transfer varying with the ambient temperature and solar radiation during a year. The hermetically sealed gas cavity between glass panels is modelled by finite elements and the stress is analyzed when the gauge pressure is maximum positive or negative due to gas temperature change at different seasons. The influence of the primary and secondary sealant of IGU is discussed. The combination of loadings due to thermal expansion and to cavity pressure is analyzed. Important conclusions about IGU structure and its durability are drawn.